1. Field of the Invention
The invention relates to a thermo-optic wave-guide switch, and more particularly to a thermo-optic wave-guide switch triggered by heating a multi-mode wave-guide.
2 . Description of the Related Art
FIG. 1A schematically shows a conventional optical switch. As shown in FIG. 1A, the conventional optical switch 10 has a Mach-Zehnder Interferometer 2 formed by a pair of optical wave-guides 1a, 1b and covered with a heater 3. When the heater 3 heats one of the optical wave-guides 1a, 1b, the output of the optical switch 10 is periodical. FIG. 1B schematically shows the periodic output of the conventional optical switch corresponding to different levels of output from the heater. As shown in FIG. 1B, the conventional optical switch 10 is an analog optical switch.
However, one disadvantage of the analog optical switch is that the output intensity thereof corresponding to the heat power is periodic and thus sensitive. In other words, the slight variation of the heat power of the heater causes huge variation of cross-talk. Furthermore, another disadvantage of the analog optical switch is susceptible to wavelength, and then the wavelength range applied to the analog optical switch is rather limited. Moreover, large volume analog optical switches have other disadvantage.
FIG. 2A schematically shows another conventional optical switch. As shown in FIG. 2A, another conventional optical switch 20 has a Y-type wave-guide 4, and the branches of the Y-type wave-guide 4 is covered with a heater 5. When the heater 5 selectively provides one branch of the Y-type wave-guide 4 with heat, the output port of the optical switch 20 is switched according to the mode-evolution theory. FIG. 2B schematically shows the output condition of the conventional optical switch corresponding to different levels of output from the heater. As shown in FIG. 2B, the conventional optical switch is a digital optical switch.
However, the disadvantage of the digital optical switch is that providing the branches of the Y-type wave-guide with huge index difference needs too much heat.